Orthotropic elastic behaviors and yield strength of fused deposition modeling materials: Theory and experiments

This work is devoted to study the mechanical behaviors of polylactic acid (PLA) materials from additive manufacturing, and an orthotropic model is established to predict the mechanical properties under arbitrary printing orientation. Firstly, the morphology of PLA material is analyzed by using scanning electron microscopy, from which the orthotropic behavior of PLA material is obtained. Three printing planes are adopted, and on each printing plane different printing angles may be selected. The mechanical parameters, including Young's modulus, yielding stress, and Poisson's ratio, for material under different printing directions are determined via quasi-static experiments. Secondly, the orthotropic constitutive model of PLA materials under different printing angles is thus obtained, and the prediction method of orthotropic mechanical properties is built based on the coordinate transformation matrix, where the orthotropic coordinate transformation matrix is acquired by attitude angles (i.e., Euler angle, the rotation angle of the local coordinate system relative to the global coordinate system). Finally, the theoretical prediction method was verified, and high-quality printing methods were recommended. In addition, the obtained results of the model show that: for PLA material, the orthotropic hypothesis model is superior to the transverse isotropic hypothesis one. This present method is not only suitable for predicting the constitutive model of printed specimens in any direction but also for other materials of fused deposition modeling.